vibrations

Rami sadeh wrote:

When cruising, this is the recommended RPM according to the manufacturer's instructions

Just a thought;

The manufacturer of the engine is Rotax - if you want the best life & performance from your engine, it behoves you to go by the Rotax recommendations.

We have a similar problem with ours. 912uls in a Eurostar. Levelled off at 1000’ at full power and sudden severe vibtation which lasts 2 to 3 secs then stops and starts again after 2 or 3 seconds. Bringing power below 4000 rpm stops it and engine is once again silky smooth. When it happens, I can see the back of the prop blades. Can have several flights between these events, all normal. Been told that its NOT the gearbox, but it feels like the clutch is slipping and the dog teeth are chattering. Help appreciated.

Speculation:

If the problem is not wheel rotation, gear box, prop set up (balance/pitch) etc, it could be that there is a sympathetic resonance occurring between engine & prop speed - some engine prop combinations, specifically advise against operations within certain RPM's.

A good quality dynamic prop balance may help, if it doesn't, just avoid this RPM range.

I don't  think it wheels because you're  in level flight. My bet is have the gearbox checked anyway by a service center and then balance the prop. 

I don't  think it wheels because you're  in level flight. My bet is have the gearbox checked anyway by a service center and then balance the prop.